P1 is a plasmid in the prophage state. When transmitted as a bacteriophage it mediates generalized transduction of bacterial genes. During this latter process the presence of specialized transducing derivatives, P1std, is sometimes detected. The P1std have acquired bacterial genes (sometimes at a loss of some P1 genes) as an integral component of a genetically hybrid chromosone. The primary goal of my research is to assess how the bacterial genes are acquired by the P1 chromosone. At this point the research program has two primary constituents. As one, the P1 chromosone and its replicative intermediates are being characterized. Analytical methods include DNA cleavage analysis, sedimentation velocity fractionation, isopycnic fractionation, and electronmicroscopy. A primary intent is to identify the sites of action controlling the formation of replicative intermediates and the identification of the topological structure of these intermediates. A primary possibility to be tested is the following - a site governing concatemer formation also has a role in P1std formation. The second constituent is the isolation and characterization of mutants with altered characteristics for P1std formation. Such mutants will be sought directly. Also mutants with blocks in P1 chromosonal formation are being independently isolated. If mutations affecting Plstd formation also affect concatemer formation, and vice versa, the functional relatedness of the two processes will be established. More refined analyses of the functions underlying concatemer formation would then be initiated.